TIPP refers to training inside public practice, i.e., with a traditional auditing firm. If you choose this route for your articles, you will gain most of your experience in the traditional auditing function. This is the type of programme you will do if you wish to pursue a career as an auditor.
TOPP is training outside of public practice. This type of programme is offered by non-auditing firms and encapsulates many different industries, including retail consumer goods, financial services, management consulting and tax consulting.
A key difference between the two is that a TIPP programme generally provides you with high-level exposure to many different businesses and industries, depending on your individual assignments within the audit team. A TOPP programme, on the other hand, will provide you with in-depth exposure to the specific business/industry where you are completing your articles.